EP0184864A1 - Cast construction parts for internal-combustion engines incorporating reinforcing elements, and method for producing the connection between the parts and the elements - Google Patents

Abstract

In the case of components made of light metal for internal combustion engines which delimit the combustion chamber, reinforcement bodies formed from non-woven ceramic fibers are cast into the surface areas subject to wear. In order to achieve a long-term protective effect against damage to the light metal lying under the reinforcement bodies, it is provided to impregnate the open pores of the fiber structure on the stress side with a layer of a ceramic mass and on the stress side with the light metal of the component.

Description

The invention relates to cast components which delimit the combustion chamber for internal combustion engines, such as pistons and cylinder heads, preferably consisting of light metal material, in the reinforcement bodies of which are formed by non-woven ceramic fibers or whiskers and which are subject to wear and / or high thermal stress, and a method to establish the connection between the components and the reinforcement bodies.

The considerable increase in the specific performance as well as the service life, operational safety and economy of internal combustion engines requires that their, in particular also those components that delimit the combustion chamber, such as pistons and cylinder heads, be designed to meet the demands placed on them. The stress on the piston essentially consists of the mechanical load from the gas pressure and the thermal load from the high temperature level as well as stresses from the temperature gradient. To master the high thermal load, the piston can be provided with a cold room. However, this generally does not contribute to reducing the thermal stresses, since the temperature gradient in the vicinity of the cold room is increased. Incidentally, the use of piston cooling contradicts the attempt to reduce the loss of heat from the combustion process to the coolant and the lubricating oil. On the other hand, this leads to high thermal loads on the piston crown.

The rim edge of a piston with a combustion chamber bowl in the piston crown is subject to a particularly critical stress condition. The accelerated flow of the combustion gases increases the heat transfer in this zone, but the heat dissipation is hindered. This increases the temperature of the bowl rim and, together with the large tangential stress from the temperature distribution, leads to over-elastic stress. When the load cools down or the internal combustion engine is switched off, residual tensile stresses develop. Since this operation occurs often occur at the bowl rim thermal fatigue cracks, which can be extended to great depth and in run at refrigerator piston in the refrigerator, which urchblasen to the _D leads the combustion gases.

Susceptibility to wear of the ring grooves on the piston, especially the uppermost ring groove, with risk of breakage of the piston rings, if, due to the overall design of the internal combustion engine, the temperatures in the ring field are abnormally high, extreme residue fuel is used, the piston play should be large for special reasons was and thereby tilting movements are made possible or air filtering, especially in dusty environments, e.g. on construction sites, is inadequate.

To a limited extent, the piston crown and bowl rim can be relieved by constructive optimization and reduction of the stresses from gas force and temperature distribution.

The reinforcement of the bowl rim by a cast nickel alloy cast iron ring provides for limited term remedy (expertise Automotive Technology, 2. _A ufl., Holland + Jose Hans Verlag, Stuttgart 1982, p 27). Permanent deformation shows a gap between the cast iron ring and the piston crown after prolonged operation. Further disadvantages of this reinforcement of the bowl rim are an increase in the weight and manufacturing costs of the piston. Instead of the cast iron ring, a ring made of aluminum titanate has therefore been proposed (D _E -O _S 32 30 388), which, however, can only be used if this ring - due to the shrink connection - has a sufficiently large area against the piston material surrounding it can support. In the search for alternative solutions which avoid the disadvantages mentioned, can also be metallic and metal-ceramic flame and plasma spray coatings on the _K olbenbo- the applied (DE-OS 31 37 731). However, the layer structure is disturbed at the sharp edges of the combustion chamber bowl edge. In addition, the layers show insufficient adhesive strength in special stress cases. The reason for this are the high thermal loads with the result of gradual softening and cracking and the large, correspondingly high stress-producing temperature gradient in the top layer itself. Finally, it is also known (DE-OS 25 07 899), piston crowns with a thickness of 30 to 80 μm To coat hard anodized layer, which results in a significantly improved protective effect against thermal fatigue, but no significant temperature reduction is achieved. It should also be pointed out to a piston (Diesel Progress _N orth America April 1984) with a cover made of sheet steel with a steel wire mesh sintered away from the stress. The cover is cast together with the piston in a press-molding process. This piston has only limited thermal insulation and a weight which is increased by the cover and the steel wire mesh.

When the risk of wear of the annular grooves so-called ring carrier pistons are used, is in which, inserted in the group consisting of an aluminum piston alloy _K olbenkörper in the region of at least the uppermost piston ring groove, an existing from an iron material ring carrier in the piston ring groove, is poured over an intermetallic compound layer (Technical Handbuch, Karl Schmidt GmbH, Neckarsulm 1967, pp. 106 to 107). The cast-in ring carrier disadvantageously increases the weight of the aluminum piston. Another reinforcement consists in piercing a groove in the area of the ring field of a piston made of an aluminum alloy and first spraying it out with a thin intermediate layer made of molybdenum, titanium, cobalt, nickel or their alloys as well as stainless steel using the metal spraying method, then with a stainless steel Fill steel with a high chromium content and a certain nickel content and then form the ring grooves (DE-OS 14 00 115). The disadvantage is that there is poor adhesive strength between the aluminum alloy and the sprayed-on intermediate layer.

GB-PS 2 106 433 describes a light metal piston produced by pressure casting, in the bottom of which a layer of fibers or whiskers is embedded to avoid cracks. Finally, according to EP-OS 80 562, to protect against wear and / or thermal fatigue cracks in components made of light metal material, non-woven ceramic fibers with a volume fraction from 2 to 10% stored. Wear resistance and thermal insulation of such pistons or components do not meet the requirements.

Object of the present invention is, therefore, ewehrungskörpern cast, the combustion chamber defining components for internal combustion engines, such as pistons and cylinder heads with _cast-B which have a structure formed from non-woven ceramic fibers or whiskers for surface protection against wear and / or thermal insulation To provide, which ensure long-term protection against damage to the underlying light metal material of the component in a relatively thin zone near the surface of the components.

This object is achieved in that the open pores of the fiber or whisker structure in the stress-side section with a layer of a low porosity hardened ceramic mass, in the stress-away section with a layer of the light metal material and in the transition area with a layer of ceramic mass and light metal material are filled, the fibers or whiskers have a diameter of 0.5 to 5 _JU m and a diameter to length ratio of 10 to 100 and have a volume of 10 to 50%, based on the total volume of the _B ewehrungskörpers occupy.

The open pores of the stress-releasing section of the fiber or whisker structure are completely impregnated with the light metal material of the component, so that a connection between the ceramic layer formed by the hardened ceramic mass and the light metal material of the component is ensured by the fibers or whiskers, both of which Forces can be transmitted perpendicular to and in the connection plane. It is assumed that according to the prior art between the kera mix or metallic matrix and the fibers or whiskers there is a sufficiently strong bond. An additional connection is achieved at the comparatively large interface between fiber or whisker reinforced ceramic mass and fiber or reinforced light metal material of the component in that the light metal material of the component penetrates so deeply into the open pores of the fiber or whisker reinforced ceramic layer that In addition to the atomic binding forces at the interfaces, the mechanical interlocking caused by the irregular shape of the pores increases the adhesive strength. The fiber or whisker structure in the section of the ceramic layer significantly improves the adhesive strength of the ceramic layer in the event that it should crack as a result of overloading, for example due to excessive thermal stresses. The fibers or whiskers prevent or delay crack propagation, at least because of their higher strength than the ceramic layer. Even if the cracks pass through the ceramic layer, there is no danger of pieces of the ceramic layer becoming detached, since each piece is firmly connected to the cast component via fibers or whiskers and the light metal material of the component engaging in the open pores. Another advantage can be seen in the fact that the fibers or whiskers bring about an equalization of the thermal expansion coefficients of ceramic mass and light metal material and thus the temperature changes inevitably associated with operation lead to significantly lower stresses in the connecting zone of the materials.

The fibers or whiskers appropriately occupy a volume of 10 to 30%, based on the total volume of the reinforcement body, and can be arranged either randomly or in such a way that they are in the claims side The section of the reinforcement body runs mainly parallel to the surface.

A preferred embodiment of the invention consists in that the fiber or whisker volume fraction of the reinforcement body increases, preferably continuously, in the direction of loading, and the volume fraction of the fiber or whisker structure in the area close to the stress is> 50 vol.%, Preferably up to 70 vol.%. In special cases it is possible that this fiber or whisker structure is free of ceramic mass.

The fiber or whisker structure is impregnated in the section on the load side to a depth of 1 to 20 mm, preferably 3 to 5 mm, with ceramic material.

The reinforcement body can also have a cover layer made of ceramic mass on the load side.

The transition area of the reinforcement body consisting of ceramic mass and light metal material has a layer thickness of almost zero to almost the thickness of the ceramic layer, preferably of 0.5 to 3 mm.

So that the shape of the fiber or whisker structure is retained when it is poured into the component made of light metal material, it is appropriate to sinter the fibers or whiskers at their points of contact with one another or to glue them with an inorganic adhesive.

It is advantageous that the ceramic layer has a low open porosity, through the pores of which the air contained in the fiber or whisker structure can escape during the impregnation with the light metal material and light metal can penetrate, at least partially, into the pores in order to achieve the positive connection to reinforce.

In order to impregnate the portion of the fiber or whisker structure away from the stress with the light metal material of the component, the liquid light metal material is cast under pressure, for example by casting presses, vacuum infiltration or the like, and the pressure or negative pressure is maintained until the light metal material solidifies.

The invention is illustrated by way of example in the drawing.

1 shows a partial longitudinal section through a light metal piston 1 with a combustion chamber trough 2 for diesel engines, the piston crown 3 and combustion chamber trough 2 of which are formed by a cast-in reinforcement body 4 according to the invention. The reinforcement body 4 consists of a fiber structure body with irregularly arranged Al ₂ O ₃ fibers with an average diameter of 3 μm and a diameter-length ratio of 10 to 100. The fiber structure is hardened on the combustion chamber side to a depth of 3 to 5 mm Si0 ₂ soaked. The open pores of the fiber structure are completely filled with light metal material 5 from the opposite side.

The structure of the cast-in reinforcement body 4 is shown in FIG. 2 in an enlarged detail from FIG. The hatched fiber structure 6 is impregnated in the combustion chamber section 7 with the hardened ceramic mass consisting of SiO ₂ , the penetration depth of which extends irregularly into the transition region 8. In the section 9 facing away from the combustion chamber, the pores of the fiber structure 6 and the open pores of the ceramic layer are impregnated with light metal infiltrated by casting presses. This creates an excellent mechanical clamp between the ceramic layer and reached the light metal material 5. Combustion chamber side, the _B ewehrungskörper 4 to an existing from the ceramic mass topcoat 10th

Claims (12)

1. Cast components which delimit the combustion chamber for internal combustion engines, such as pistons and cylinder heads, preferably consisting of light metal material, in whose reinforcement bodies formed from non-woven ceramic fibers or whiskers, which are subject to wear and / or high thermal stress, are cast in, characterized in that the open pores of the fiber or whisker structure (6) in the stress-side section (7) with a layer of a low porosity hardened ceramic mass, in the stress-side section (9) with a layer of the light metal material (5) and in the transition area (8) are filled with a layer formed from the ceramic mass and the light metal material, the fibers or whiskers have a diameter of 0.5 to 5 μm and a diameter-length ratio of 10 to 100 and a volume of 10 to 50%, based on the total volume of the reinforcement body rs (4). 2. Cast components according to claim 1, characterized in that the volume of the fibers or whiskers is 10 to 30%, based on the total volume of the reinforcement body (4). 3. Cast components according to claims 1 and 2, characterized in that the fibers or whiskers are arranged randomly. 4. Cast components according to claims 1 and 2, characterized in that the fibers or whiskers in the stress-side section (7) of the reinforcement body (4) run predominantly in parallel to the surface. 5. Cast components according to claims 1 to 4, characterized in that the reinforcement body (4) in the stress-side section (7) to a depth of 1 to 20 mm, preferably 3 to 5 mm, are impregnated with ceramic mass. 6. Cast components according to claims 1 to 5, characterized in that the volume fraction of the fibers or whiskers of the reinforcement body (4) increases in the loading direction, preferably continuously. 7. Cast components according to claim 6, characterized in that the volume fraction of the fiber or whisker structure in the stress-related section is> 50%, preferably up to 70%. 8. Cast components according to Claims 1 to 7, characterized in that the possesses from ceramic mass and _L eichtmetallwerkstoff transition region (8) formed a layer thickness mm from near zero to the thickness of the ceramic layer, preferably from 0.5 to third 9. Cast components according to claims 1 to 8, characterized in that the fibers or whiskers are sintered or glued together at their points of contact. 10. Cast components according to claims 1 to 9, characterized in that the reinforcement body (4) on the stress side has a cover layer (10) made of the ceramic mass. 11. Modification of the cast components according to claim 7, characterized in that the fiber or whisker structure in the portion close to the stress is free of ceramic mass. 12. A method for producing the connection between cast components and the reinforcement bodies according to claims 1 to 10, characterized in that the stress-side portion of the fiber or whisker structure is soaked under pressure with the molten light metal material and the pressure is maintained until the melt solidifies remains.

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